Islamic State (IS, previously ISIS/ISIL) has been operating training camps for attacks on the West, providing longer training and more autonomy to its recruits, AP reported, citing European and Iraqi intelligence officers as well as a French lawmaker.

Terror cells have been reportedly set up all across Europe and their main goal is to carry out as many attacks as possible, not just to kill as many people as possible – all in order to force European authorities to spend more money, the report said.

Leaders of these terrorist cells appear to be French-speaking individuals with links to North Africa, France and Belgium, according to a European security official who talked to AP on condition of anonymity. They are usually tasked with creating new attack strategies in Europe, he said.

When IS claimed responsibility for Tuesday’s attacks on Brussels, the extremist group mentioned a “secret cell of soldiers” that was sent to Brussels.

This kind of structure has also been confirmed by the EU police agency, Europol, which said in January that IS had “developed an external action command trained for special forces-style attacks.”

The training of the recruits seems to be a priority now, as it reportedly went from a short span of just a few weeks to a much longer time period. It also started to include battleground strategies, explosives, surveillance techniques and counter-surveillance, according to the security official.

“The difference is that in 2014, some of these IS fighters were only being given a couple weeks of training,” he said. “Now the strategy has changed. Special units have been set up. The training is longer. And the objective appears to no longer be killing as many people as possible but rather to have as many terror operations as possible, so the enemy is forced to spend more money or more in manpower.”

Moreover, it came to light that IS sometimes reuses terror cells. For example, IS militants who were involved in the Paris attacks have spread out across Europe, leaving for Germany, Britain, Italy, Denmark and Sweden, a senior Iraqi intelligence official said.

French Senator Nathalie Goulet, co-head of a commission tracking jihadi networks, estimated that anywhere from 400 to 600 IS fighters are being trained specifically for external attacks. She also said that around 5,000 Europeans have left the continent to go to Syria and join IS.

“The reality is that if we knew exactly how many there were, it wouldn’t be happening,” Goulet said.

The training camps are reportedly located in several countries, including Syria, Iraq and some unidentified “former Soviet bloc states.” Islamic State is also now giving its cells more control over when and how to proceed.

AP’s sources believe that the attacks on Brussels were a response to the arrest of the fugitive Salah Abdeslam, which happened just a few days earlier.

“To pull off an attack of this sophistication, you need training, planning, materials and a landscape,” Shiraz Maher, a senior research fellow at the International Centre for the Study of Radicalisation at Kings College in London, told the news agency. “Even if they worked flat out, the attackers in Brussels would have needed at least four days.”

After the attacks on Paris in November, Abdesalam fled and managed to create a new network, while hiding out in his childhood neighborhood of Molenbeek, Belgium, which has a large Muslim population, Belgian officials said.

“Not only did he drop out of sight, but he did so to organize another attack, with accomplices everywhere. With suicide belts. Two attacks organized just like in Paris. And his arrest, since they knew he was going to talk, it was a response: ‘So what if he was arrested? We’ll show you that it doesn’t change a thing,’” Goulet added.

Belgian authorities fear that one fugitive connected to Tuesday’s attacks in Brussels might follow the same path as Abdesalam. They discovered that a man in a white jacket, who was caught conversing with two suicide attackers on security footage, was able to disappear.

Tuesday blasts that rocked Brussels’ Zaventem Airport and the city’s Maalbeek Metro station, killing at least 31 people and injuring about 300. Two Brussels airport suicide bombers have been identified as Belgian-born brothers Khalid and Brahim El Bakraoui.

The third suspect, the bombmaker, has been named as Najim Laachraoui. He reportedly made his explosives out of regular household items. French and Belgian officials told AP that Laachraoui also made suicide vests for Paris attacks. Authorities said that DNA evidence points to the likelihood that he died during Brussels attacks.

'Ordered to strike when they see fit'

An American intelligence official speaking to The Mirror estimated the number of possible independent ISIS cells in Europe at more than 100. According to the source, the FBI has been working closely with the Belgians on identifying “a wider network” of terrorists operating in Europe.

Similar to the other estimates, the Americans believe around 450 bomb makers and other experts could have already received orders to carry out attacks at will: “They are to carry out coordinated attacks in their cells, but are left to decide a time and place of their choosing,” the source told the British newspaper on condition of anonymity.